Low profile antenna



April 9, 1966 J. M. BOYER 3,247,515

LOW PROFILE ANTENNA Filed March 4, 1965 2 Sheets-Sheet 1 Apnl 19, 1966 J. M. BOYER 3,247,515

LOW PROFILE ANTENNA Filed March 4, 1963 2 Sheets-Sheet 2 b 37a. 40 43a.

7 aria United States Patent C 3,247,515 LGW PRGFELE ANTENNA Joseph M. Boyer, Rolling Hills, Califi, assignor to Northrop Corporation, Beverly Hills, Calif., a corporation of California Filed Mar. 4, 1963, Ser. No. 262,593 15 Claims. Cl. 343-742) This invention relates to antennas for radio wave sending and reception and particularly to a directly driven resonant radiator, hereinafter referred to as a DDRR, for "use from the lowest radio frequencies up to and including approximately 3,000 megacycles, depending on the physical dimensions of the antenna.

The usual sending and receiving equipment is designed to operate efficiently on all bands within the short wave region, but usually in order to operate efficiently on all of these bands the operator requires separate antennas for each band and thereby great areas of land need to be employed for the erection of such separate antenna systems. These same considerations apply as well to all other situations in which it is desired to send and receive signals selectively on a plurality of discrete wavelengths with a minimum of antenna equipment and with maximum efficiency on each of the wavelengths involved.

The present state of the antenna art includes antennas of special geometry and large overall cross section in terms of wavelength which may be used over wide frequency bands while maintaining substantially constant input impedance with resulting good impedance match to the transmission line connected to the antenna terminals, but such antennas are practical only on the very high, ultra high and microwave frequency bands and are impractical for frequency bands between 1 to 30 mega- -cycles or lower, for example, due to the fact that the resulting structures would be so large as to be prohibitive both from size and cost standpoints.

Having the foregoing considerations in mind, a principal object of the invention is to provide a single antenna which will permit the transmission and reception of radio signals over a frequency span of at least two to one while maintaining at its input terminals a substantially constant input impedance on each of the frequencies lying within the frequency span for which it is designed.

Another object of the present invention is to provide an efiicient, resonant antenna which is vertically polarized, and eliminates the need for structures of great vertical height.

A further object is to provide an antenna in which loading means is applied at a point of small current so that vexious power losses can be minimized.

It is a still further object to provide an antenna which radiates a vertically polarized wave when mounted parallel to the earth plane, with a distribution of radiated energy essentially the same as that produced by a quarterwavelength vertical radiator.

Another object of the present invention is to provide an antenna construction embodying the former objectives which is simple, of pleasing appearance, which is sufficiently rugged to withstand adverse weather and other conditions, and which may be installed and erected in limited space areas.

Yet another object of this invention is to provide an antenna construction having the above objectives which affords strong rejection of interference resulting from radio signals occupying frequencies closely adjacent to the frequency being employed.

Other objects and features of advantage of this invention will become apparent upon reading the detailed description of specific embodiments to follow, and it is to be understood that these embodiments are for illustration only and may be modified by persons skilled in the art while still employing the basic principles defined.

Briefly, my present invention in one form comprises two circular conductive members parallel to each other and arranged so that the instantaneous current in each member is opposite to the current in the corresponding "portions of the other member. In another form, my invention comprises only one such conductive member mounted parallel to a conductive plane, with a perpendicular conductive post or leg connected therebetween. Means are provided to feed a signal into (or out of) the antenna, tune the antenna to resonance, and match the antenna input impedance to a transmission line. The antenna is preferably mounted with the said members parallel to the earth plane. These members need not be circular, but may form the sides of a plane polygon.

In the accompanying drawings,

FIGURE 1 is a perspective view of a balanced antenna structure embodying the present invention, mounted on a mast and elevated above the earth.

FIGURE 2 is a perspective, broken away view of a conducting plane member such as the roof of a vehicle, showing an unbalanced antenna structure embodying the present invention.

FIGURE 3 is a diagrammatic view of a balanced antenna structure embodying the present invention, showing the directions of current flow in the conductive members.

FIGURES 4, S, and 6 are diagrammatic views showing further antenna embodiments of the present invention.

Referring to the form of the DDRR invention shown in FIGURES 1 through 3, the illustrated embodiment comprises an upper circular conductive member 10 conductively joined at its extremities, including a linear conductive member 11 conductively joined at one point to circular member 10, disposed in the same plane as that containing the circular member 10, projecting inward radially and directed at the origin of said member, said circular member 10 disposed above a second, lower circular member 12 lying within a plane parallel to that containing the upper circular conductive member 10, and having a second linear conductive member 14 similar to the first linear member 11, supported and aligned by nonconductive separator members 15, first capacitor means 16 joining upper circular member 10 to lower circular member 12 at the points of the respective conductive joints between the linear conductive members and the circular members, said upper and lower circular conductive members 10 and 12 being additionally joined by a second capacitor means 17 at a point diametrically opposite the first capacitor means 16, each linear conductive member 11 and 14 carrying a terminal connector means 19 in the form of a threaded screw for example at its extremity, a balanced two wire transmission line 20 being terminated into the connector means 19 of linear conductive members 11 and 14 respectively and joining the antenna to a remotely located radio apparatus 21, the collective antenna assembly being supported on a mast 22 by a tripod of nonconductive support members 24 rigidly fixed to lower circular member 12 by means of clamping -means 25 and at the mast top by a collar member 26.

In the specific embodiment of the invention above described the following dimensions are indicated in terms of the relationship existing between the physical extent and the operating wavelength extremes of the radio bands being transmitted or received as noted by corresponding letters applied to FIGURE 1, such dimensions being understood to apply equally to the embodiments disclosed in FIGURES 2 and 3.

Referring to the balanced embodiment shown in FIG- URE l, the currents in the balanced two wire transmission line are equal and electrically one hundred eighty degrees out of phase. Applied to the extremities of the upper and lower linear conductive members 11 and 14, as shown in FIGURE 3, currents 27 and 28 flow along the circular conductive members 10 and 12 anti-symmetrically and one hundred eighty degrees out of electrical phase with one another.

It will be appreciated by those skilled in the antenna art that electrical waves caused to be radiated by the said out-of-phase currents in the upper and lower circular members 10 and 12 will be polarized so that the electric components of the signal will be disposed parallel to the circular members 10 and 12. Such skilled practitioners will further understand that these conditions will remove or cancel such parallel and out-of-phase radiation signals in the region remote from the antenna so that distant receivers would not be energized. This unique property of the invention differs from antennas of the prior art such as the single circle or loop which may superficially resemble a portion of this invention.

Under conditions of the preferred embodiment of the invention herein disclosed, the reactance of the first capacitor means 16 at the higher frequency limit for which the total diameter noted in FIGURE 1 as dimension a is 0.16 wavelength, shall be small, where as the shunt reactance of second capacitor means 17 shall be such as to produce electrical resonance and greatest radiation efficiency. For the other limiting condition where the antenna dimension a is 0.08 wavelength at the selected operating frequency, the reactance of first capacitor means 16 is preferably adjusted to some low but noncritical magnitude and second capacitor means 17 is adjusted for resonance in accordance with recognized techniques, the exact value depending on equivalent line length and the value of the first capacitor means 16.

In the specific example of the invention above described, a preferred embodiment is indicated by an approximate extent of 0.003 wavelength for linear conductive members 11 and 14 when terminated in a lOO-ohm characteristic impedance for transmission line 20. For the preferred embodiment, a voltage standing wave ratio not exceeding 2:1 will be found by measurement when tuning the frequency band range for which the relationship a:0.l6 wavelength to (1:008 wavelength obtains.

Referring next to the modified form of the invention shown in FIGURE 2, the modification comprises a circular conductive member 10a uniformly disposed and spaced parallel to the surface of a conductive plane by means of nonconductive supports 31, adjusted to suitable operational conditions as above described by capacitor means 16a. and 17a, linear conductive member 11a being conductively joined to the inner conductive wire 32 of an unbalanced coaxial transmission line 34, the outer conductive sheath of coaxial transmission line 34 being conductively joined to the surface of the conductive plane 30, said coaxial transmission line 34 serving as the means for connection to the remotely located radio equipment Zia. An aperture 35 is provided in the conductive plane 30 for leading the coax line 34 therethrough.

In the embodiment shown in FIGURE 2, the spacing between the circular conductive member 10a and the conductive plane 30 will be one half that described above to be equivalent to the balanced embodiment shown in FIGURE 1, the characteristic impedance of coaxial line 34 being 50 ohms. A larger spacing will result in increased efiiciency.

A variation of the DDRR antenna is shown in FIG- URE 4. Here, a circular antenna member 36 is not fully closed, but. has two integral conductive legs 37 and 38 at the nearly closed ends of the member 36, the legs being bent downwardly to conductively join a ground plane 40. Antenna member 36 is parallel to the plane 40 and is further supported over it by nonconductive posts 41. From the top of the first leg 37, a conductive linear extension 42 is connected to the antenna ring member 36 and extends toward the center of the ring a short distance, similar to linear member 11 in FIGURE 1.

A tuning capacitor 44 is connected from the side of ring member 36 diametricaliy opposite extension 42 to ground palne 40. One conductor 45 of a coaxial cable 46 is attached to the free end 47 of extension 42. and the other conductor (sheath 49) is grounded preferably near the first conductor connection at extension end 47. At the far end of coaxial cable 46, a radio set 50 is connected.

With a single ring 36, the equivalent spacing between it and the ground plane 40 is again one-half of that described for FIGURE 1. When the circumference of the ring member 36 is one-half wavelength or less, the current distribution is as shown by arrows 43.

A further embodiment is shown in FIGURE 5, where an open ring member 36a is provided with grounded end legs 37a and 38a, and a tuning capacitor 44a similar to FIGURE 4, supported over ground plane 40. In this case, the coaxial cable 46a is coupled to the antenna through a coupling collar 51 connected to ring 36:: a short distance from the first leg 37a. This distance j is for the purpose of correct impedance matching between the antenna and the tranmission line, and is adjusted to equal about .0007 wavelength for a coaxial cable impedance of 50 ohms. This distance may vary over a large range. Arrows 43a again show the instantaneous current directions.

To provide operation over a wider frequency band, the alternate construction of FIGURE 6 can be employed. This is similar to FIGURE 5 with the addition of a sec ond ring member 36c concentric and coplanar with a first ring member 36b. In this case, the inner conductor 45.: of coaxial cable 46b is split into two substantially equal portions, one connected to each ring at respective collars 51b and 510. Two tuning capacitors 44b and 440 should also be used. The lower ends of conductive support legs 37b, 37c, 33b and 38c are fastened to a conductive plate 52 forming a portion of the ground plane 40.

In all the present structures such as shown in FIG- URES 2 and 46, a metal plate similar to plate 52 may be used. This plate may advantageously be the metal top of an automobile or other vehicle upon which the present antenna is installed. In the case of large antennas erected over the earth, an effective ground plane may be formed by a system of interconnected bare wires placed at ground level.

It has been found that the antenna invention disclosed generates signals throughout all directions of the compass in the horizontal plane equally, the electric polarization being vertical.

It is obvious that many modifications, additions, and variations can be made to the present invention in the light of the teachings disclosed herein, without avoiding the basic structure involved. For instance, the specific DDRR antenna configurations described and claimed in my copending application Serial No. 206,248,

filed June 29, 1962, now Patent Number 3,151,328, issued September 27, 1964, are examples of such further constructions based on the presently disclosed and claimed development. Moreover, as mentioned previously, the ring members of this antenna may be in the form of straight sides of a substantially regular polygon of three or more sides, although such an antenna of four or more Sides has preferred performance. Further, the ring members may be of either solid or tubular material, and the structural'shape of the rings which is bent into an overall circular form is not limited to a simple cylindrical shape. The tuning capacitors such as 17 and 44 may obviously all be made variable so that optimum resonance adjustment can be made;

While in'order'to comply with the statute, the invention has been described in language more or less specific as'to structural features," it is to be understood that the invention is not limited to the specific features shown, but that the method and means herein disclosed comprise several forms of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

I claim:

1. An antenna comprising a horizontal, conductive closed ring member, a linear conductive stub member joined at one end to said ring member and extending radially toward the center of said ring member in the same plane therewith, a substantially conductive plane member spaced below and parallel to said ring member, a first capacitor means connected between said ring member and said plane member at a location diametrically opposite said stub member, a second capacitor means connected between said ring member and said plane member at the junction of said stub member and said ring member, a first transmission line connection point at the free inner end of said stub member, and a second transmission line connection point on said conductive plane member.

2. Apparatus in accordance with claim 1 wherein a coaxial transmission line extends upwardly through said plane member, the inner conductor of said coaxial line being connected to said first connection point, and the conductive sheath of said coaxial line connected to said plane member.

3. An antenna comprising a pair of circular, conductive, closed ring members spaced parallel to each other, a pair of linear conductive stub members joined respectively at their ends to said ring members at corresponding respective points thereon, each of said stub members extending radially toward the center of its respective ring member in the same plane therewith, a first capacitor means connected between said ring members at a location diametrically opposite said stub members, a second capacitor means connected between said ring members at the respective junctions of said stub members and said ring members, and a transmission line connection point at the free inner end of each said stub member.

4. Apparatus in accordance with claim 3 including nonconductive separator members holding said ring members in spaced position, non-conductive antenna support members fixed to one of said ring members, and a vertical mast member attached to said support members.

5. An antenna comprising a conductive ring member having spaced extremities, a pair of conductive leg portions joined respectively at their first ends to said extremities, and the other ends of said leg portions connected to a grounded plane parallel to said ring member, said leg portions being perpendicular to the plane of said ring member, a linear conductive stub member joined at one end to one extremity of said ring member and extending radially toward the center of said ring member in the same plane therewith, capacitor means connected from a point on said ring member diametrically opposite said extremities to said grounded plane, a first transmission 6 1 line feed point at the free inner end of said stub member, and a second line feed point on said grounded plane.

6. An antenna comprising a conductive ring member having spaced extremities, a pair of conductive leg portions joined respectively at their first ends to said extremities, and the other ends of said leg portions connected to a grounded plane parallel to said ring member, said leg portions being perpendicular to the plane of said ring member, capacitor means connected from a point on said ring member diametrically opposite said extremities to said grounded plane, a first transmission line feed point on said ring member at a certain distance from one said extremity to provide impedance matching, and a second line feed point on said grounded plane.

7. An antenna comprising a plurality of conductive,

concentric, coplanar ring members each having spaced extremities, a pair of conductive leg portions joined respectively at their first ends to said extremities, and the other ends of said leg portions connected directly to a grounded plane parallel to said ring members, said leg portions being perpendicular to the plane of said ring members, respective capacitor means connected from a point on each said ring member diametrically opposite said extremities to said grounded plane, a first feed point on each said ring member, respectively, at a certain distance from one extremity thereof to provide impedance matching to one conductor of a transmission line, and a second feed point, on said grounded plane, adapted to be connected to the other conductor of said transmission line.

8. An antenna comprising a conductive circular ring member having spaced extremities, another conductive member parallel to said ring member, a pair of conductive leg portions joined respectively at their first ends to said extremities, and the other ends of said leg portions connected directly to said other parallel member, said leg portions being perpendicular to the plane of said ring member, capacitor means connected from a point on said ring member diametrically opposite said extremities to said other member, and means for connecting opposite conductors of a transmission line to said members respectively.

9. An antenna comprising a pair of parallel conductively closed ring members, said members being separated by a distance equal to from .01 to .10 times the operating wavelength, at relatively low capacitive reactance connected directly between said members, a tuning capacitance connected directly between said members diametrically opposite said low reactance, and means for connecting opposite conductors of a transmission line to said members, respectively, at the location of said low reactance.

10. An antenna comprising a conductive ring member having spaced extremities and a pair of conductive leg members joined at one end of each to said extremities, respectively, said leg members being perpendicular to the plane of said ring member, common conducting means connected directly between the opposite ends of said leg members, means for connecting one lead of a transmission line directly to said antenna, and means for connecting the other lead of the transmission line to said common conducting means.

11. Apparatus in accordance with claim 10 including a plurality of similar ring members and leg members, said leg members joined to said common conducting means, and said ring members being concentric and coplanar.

12. Apparatus in accordance with claim 10 wherein said common conducting means comprises a ground plane parallel to said ring member.

13. Apparatus in accordance with claim 12 wherein the distance between said ring member and said ground plane is from substantially .003 to .05 wavelength at the antenna operating frequency.

14. Apparatus in accordance with claim 12 including a transmission line having one lead thereof connected directly to said antenna, and the other lead thereof connected directly to said ground plane. I

15. A non-directional, linearly polarized antenna comprising a conductive ring member, another conductive member fixed parallel to said ring member, means for connecting one conductor of a transmission line to said ring member, means for connecting the other conductor of the transmission line to said parallel member, and means for bringing said antenna to resonance at a desired operating frequency, said resonance means being connected between said members at a point substantially diametrically opposite the transmission line connection to said ring member.

16. A non-directional, linearly polarized antenna comprising a conductive circular ring member, an elfectively continuous plane member at earth potential fixed parallel to said ring member, means for connecting one conductor of a transmission line to said ring member, means for connecting the other conductor of the transmission line 8 to said plane member, the total diameter of said ring member being from about .08 to about .16 wavelength at the antenna operating frequency, and the distance between said ring member and said plane member being from substantially .005 to .05 wavelength.

References Cited by the Examiner UNITED STATES PATENTS ELI LIEBERMAN, Examiner. 

1. AN ANTENNA COMPRISING A HORIZONTAL, CONDUCTIVE CLOSED RING MEMBER, A LINEAR CONDUCTIVE STUB MEMBER JOINED AT ONE END TO SAID RING MEMBER AND EXTENDING RADIALLY TOWARD THE CENTER OF SAID RING MEMBER IN THE SAME PLANE THEREWITH, A SUBSTANTIAL CONDUCTIVE PLANE MEMBER SPACED BELOW AND PARALLEL TO SAID RING MEMBER, A FIRST CAPACITOR MEANS CONNECTED BETWEEN SAID RING MEMBER AND SAID PLANE MEMBER AT A LOCATION DIAMETRICALLY OPPOSITE SAID STUB MEMBER, A SECOND CAPACITOR MEANS CONNECTED BETWEEN SAID RING MEMBER AND SAID PLANE MEMBER AT THE JUNCTION OF SAID STUB MEMBER AND SAID RING 